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Diatom frustules have species-specific patterns of pores, striae, pores, and nanopores, periodically arranged on its silica surface, as sets of cavities that modify the vacuum electromagnetic density of states. Therefore, frustules may be considered photonic crystals; the interaction with light-emitting sources inside the pores may potentially result in enhancement or inhibition of their spontaneous radiative emission rate and frequencies. In this work, we studied the photoluminescence of cadmium sulfide nanoparticles (CdS-NP) deposited inside frustule cavities that conveyed evidence of cavity-NP interaction. We synthesized CdS-NP, a semiconductor compound achieving quantum dots small enough to impose confinement effects to the electronic states. CdS-NP and their clusters were physiosorbed onto the surface, striae, and predominantly inside the pores of the cleansed frustules of Amphora sp. A broad peak with a maximum intensity at 437 nm (2.84 eV) was recorded after excitation with a 375 nm light source, showing a large blue shift and signal amplification of the CdS-NP photoluminescence when these were embedded inside the pores of the silica frustule. Using the Brus equation, we estimated a NP size of 4.1 ± 0.2 nm for the CdS-NP snuggly packed inside the smaller pores of the frustule, of 10 ± 0.7 nm in average diameter, The emission Purcell enhancement factor for an emitting atom in a cavity was calculated. The obtained Q factor (c. 5) was smaller than typical Q factors for designed semiconductor cavities of similar dimensions, an expected situation if it is assumed that the pores are open-ended cavities.

Antibiotics generally cause drug-resistant genes (ARGs) and drug-resistant bacteria (ARBs). With a complex class of antibiotics, it is very crucial to select specific adsorbents for different kinds of antibiotics. Zn-Al layered double hydroxide (LDH) and calcined layered double hydroxide (LDO) were prepared as absorbents for tetracycline hydrochloride (TCH) and ofloxacin (OFX), which were two antibiotics with different structures. According to the results of the adsorption experiments, LDO has the best adsorption capacity on TCH, reaching 322.58 mg/g. Acid-base titration, XRD, TEM, SEM, BET, and FI-TR analyses indicate that LDO has more active sites on the surface, the “memory effect”, and a larger specific surface area. In contrast, the removal rate of OFX by LDO is low because OFX has a more stable quinolone ring structure. Furthermore, after five adsorption-desorption cycles, the adsorption rate of TCH remains at 94.9%, demonstrating that LDO has good cyclic adsorption capacity for TCH. This study creatively combines acid-base buffering characteristics to study the mechanism of the adsorption of antibiotics by hydrotalcite, and proposes that LDO can be used as a special adsorbent for TCH.

In biohydrometallurgical processes, a mineral exhibits different oxidation phases due to the system's heterogeneity, especially in heap leach pads. Oxidation chemically modifies the mineral surface altering its interface, and thereby affecting the bacteria-mineral interaction, mineral reactivity and leaching velocity. Given that the mineral can be found in different oxidation states in heap bioleaching processes, three oxidation conditions of FeS2, in which iron and/or sulfur related compounds are formed on the mineral surface were assayed. This paper studies the interaction between the modified surface of a sulfide mineral, FeS2, and 0 K culture medium, typically used in biomining processes. Chemical and electrochemical changes on surfaces were characterized by subjecting them to weathering in an acidic culture medium (pH 1.8), without applying potential or current. The chemical species formed were identified by Raman spectroscopy. The modified pyrite surfaces showed significant interfacial transformations upon immersion in the culture medium, and the formation of passive chemical species, such as elemental sulfur, jarosite, phosphates and oxides, were identified. These interfacial modifications are correlated with changes in the open circuit potential (OCP) values during immersion of pyrite and surface modified pyrites in 0 K culture medium. Electrochemical characterization showed a decrease in mineral oxidation capacity, which directly affects the extent of leaching and possibly, of the interaction with other elements participating in the process, such as microorganisms. To study the interactions among bacteria and the pyrite mineral suffering different surface modifications, the attachment of the bioleaching bacterium Leptospirillum sp. was evaluated. Fil: Saavedra Olaya, Albert Ulises. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Química Biológica de la Facultad de Ciencias Exactas y Naturales. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Química Biológica de la Facultad de Ciencias Exactas y Naturales; Argentina Fil: García Meza, J. Viridiana. Universidad Autonoma de San Luis Potosi; México Fil: Corton, Eduardo. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Química Biológica de la Facultad de Ciencias Exactas y Naturales. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Química Biológica de la Facultad de Ciencias Exactas y Naturales; Argentina Fil: González, Ignacio. Universidad Autónoma Metropolitana - Iztapalapa; México

Chalcopyrite is the main ore mineral used in industrial copper extraction. However, when passivation processes occur during hydrometallurgical treatment, a large percentage of the mineral being treated is not solubilized, so the copper recovery is limited. Galvanic interactions between semiconductor minerals are the basis of many strategies to achieve a more efficient process for increasing copper dissolution. These interactions concern generally two metallic sulfides. The present study describes a new galvanic interaction between chalcopyrite-magnetite (CuFeS2-Fe3O4) in an acid microbial culture medium, used routinely in biomining processes. The electrochemical characterization of CuFeS2, Fe3O4 and a mineral containing CuFeS2-Fe3O4 is performed. Galvanic interactions are demonstrated by comparing Evans diagrams constructed from current transients obtained by imposing the potential pulses to each species studied. It is determined that CuFeS2 and Fe3O4 fulfil the role of anode and cathode, respectively, in the behavior of the corresponding mineral. Stripping voltammetry is used to quantify electro-dissolved ions; the electrooxidation of CuFeS2-Fe3O4 mineral in acid culture medium releases twice as many copper ions as pure chalcopyrite. This corroborates that the galvanic interactions prevent the formation of typical passivating components observed in chalcopyrite. Fil: Saavedra Olaya, Albert Ulises. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Química Biológica de la Facultad de Ciencias Exactas y Naturales. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Química Biológica de la Facultad de Ciencias Exactas y Naturales; Argentina Fil: García Meza, J. Viridiana. Universidad Autonoma de San Luis Potosi; México Fil: Corton, Eduardo. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Química Biológica de la Facultad de Ciencias Exactas y Naturales. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Química Biológica de la Facultad de Ciencias Exactas y Naturales; Argentina Fil: González, Ignacio. Universidad Autónoma Metropolitana - Iztapalapa; México

The relationship between erodibility (susceptibility to erosion) and soil biological parameters has not been thoroughly investigated in Palomas Valley (PV), a region in San Luis Potosi, Mexico that includes gully-eroded microcatchments. Previous reports have shown the potential of Glomalin-related soil protein (GRSP) as an erodibility marker. Thus, our first goal was to develop an optimized autoclaving-free extraction method for GRSP suitable for 1D-SDS-PAGE analysis. Samples from horizon A (0–10 cm) were collected in three sites in PV. Total GRSP and organic matter contents were obtained, and GRSP was used for correlation analysis (Pearson correlation coefficient) with the K factor, an erodibility index. Our novel total protein-extraction method allowed to obtain moderated resolution electrophoretic patterns and GRSP detection was achieved by molecular weight comparison. GRSP contents ranged 11–203 μg·g−1 soil, and organic matter contents ranged from 2.1 to 12.8%. A multiple regression analysis was performed, obtaining a strong correlation (R = 0.79; R2 = 0.63) among organic matter and GRSP contents and K factor. The results suggested a strong dependence of K from organic components, mainly from GRSP. This is the first time that K factor and GRSP correlation analysis has been reported. Also, this work provides interesting data that could improve the analysis of factor K. All these results suggest GRSP content may play an important role in soil erodibility, but further research is required.

To develop a bioelectrochemical system (BES) to couple the biooxidation of chalcopyrite (CuFeS2), bioelectrogenesis, and the cathodic Cu2+ reduction, bioanodes of acidophilic (pH

Inorganic wastewaters and sediments from the mining industry and mineral bioleaching processes have not been fully explored in bioelectrochemical systems (BES). Knowledge of interfacial changes due to biofilm evolution under acidic conditions may improve applications in electrochemical processes, specifically those related to sulfur compounds. Biofilm evolution of Acidithiobacillus thiooxidans on a graphite plate was monitored by electrochemical techniques, using the graphite plate as biofilm support and elemental sulfur as the only energy source. Even though the elemental sulfur was in suspension, S0 particles adhered to the graphite surface favoring biofilm development. The biofilms grown at different incubation times (without electric perturbation) were characterized in a classical three electrode electrochemical cell (sulfur and bacteria free culture medium) by non-invasive electrochemical impedance spectroscopy (EIS) and cyclic voltammetry. The biofilm structure was confirmed by Environmental Scanning Electrode Microscopy, while the relative fractions of exopolysaccharides and extracellular hydrophobic compounds at different incubation times were evaluated by Confocal Laser Scanning Microscopy. The experimental conditions chosen in this work allowed the EIS monitoring of the biofilm growth as well as the modification of Extracellular Polymeric Substances (EPS) composition (hydrophobic/ exopolysaccharides EPS ratio). This strategy could be useful to control biofilms for BES operation under acidic conditions.

Acidithiobacillus thiooxidans is an acidophilic chemolithoautotrophic bacterium widely used in the mining industry due to its metabolic sulfur-oxidizing capability. The biooxidation of sulfide minerals is enhanced through the attachment of At. thiooxidans cells to the mineral surface. The Type IV pili (TfP) of At. thiooxidans may play an important role in the bacteria attachment since TfP play a key adhesive role in the attachment and colonization of different surfaces. In this work, we report for the first time the mRNA sequence of three TfP proteins from At. thiooxidans, the adhesin protein PilY1 and the TfP pilins PilW and PilV. The nucleotide sequences of these TfP proteins show changes in some nucleotide positions with respect to the corresponding annotated sequences. The bioinformatic analyses and 3D-modeling of protein structures sustain their classification as TfP proteins, as structural homologs of the corresponding proteins of Ps. aeruginosa, results that sustain the role of PilY1, PilW and PilV in pili assembly. Also, that PilY1 comprises the conserved Neisseria-PilC (superfamily) domain of the tip-associated adhesin, while PilW of the superfamily of putative TfP assembly proteins and PilV belongs to the superfamily of TfP assembly protein. In addition, the analyses suggested the presence of specific functional domains involved in adhesion, energy transduction and signaling functions. The phylogenetic analysis indicated that the PilY1 of Acidithiobacillus genus forms a cohesive group linked with iron- and/or sulfur-oxidizing microorganisms from acid mine drainage or mine tailings.

Bacterial cell attachment that results in biofilm formation is the first step of bacteria-mineral interaction, and it is known that they strongly depend on the chemical characteristics of the mineral surface. In some industrial processes, like those used in biohydrometallurgy, the minerals are present in different chemical oxidation states, especially when heterogeneous low-grade ore deposits and mining tailings are used as starting materials for microbial inoculation. This study describes a strategy for monitoring bacterial attachment to pyrite (FeS2) and surface modified pyrite weathered in the culture growth medium used (pH 1.8), by means of a non-invasive electrochemical technique such as electrochemical impedance spectroscopy (EIS). The EIS evaluation of Leptospirillum sp. interaction with pyrite and surface modified pyrite weathered electrodes revealed significant changes at low frequencies, depending of the compounds presented over the four samples used, including unmodified pyrite and three surface modified samples. Once the frequency at which the adhesion process can become uncover was selected (0.1 and 0.05 Hz), the phase angle variation at such frequency was determined using different microbial concentrations. Different microbial attachment values were obtained for the different electrodes and related to the initial inoculum (2 × 108 cells/mL), as follow: FeS2/Fe(OH)n,S0 (38 ± 3.2%); FeS2/Fe(OH)n (31 ± 5.5%); FeS2 (27 ± 4.7%) and FeS2/S0 (18 ± 3.8%). Microbial attachment to unmodified and modified surfaces, evaluated by EIS, was corroborated with the traditional method of bacterial attachment evaluation by cell count in a Neubauer chamber (r2 = ~0.9). This strategy could be used in developing sensors for the fast and efficient bacterial attachment evaluation in minerals.

Acidithiobacillus thiooxidans is an acidophilic chemolithoautotrophic bacterium widely used in the mining industry due to its metabolic sulfur-oxidizing capability. The biooxidation of sulfide minerals is enhanced through the attachment of A. thiooxidans cells to the mineral surface. The Type IV pili (TfP) of At. thiooxidans may play an important role in the bacteria attachment, since among other functions, TfP play a key adhesive role in the attachment to and colonization of different surfaces. In this work, we reported for the first time the confirmed mRNA sequences of three TfP proteins from At. thiooxidans, the protein PilY1 and the TfP pilins PilW and PilV. The nucleotide sequences of these TfP proteins show changes of some nucleotide positions with respect to the corresponding annotated sequences. The bioinformatic analyses and 3D-modeling of protein structures sustain their classification as TfP proteins, as structural homologs of the corresponding proteins of P. aeruginosa, results that sustain the role of PilY1, PilW and PilV in pili assembly. Also, that PilY1 comprises the conserved Neisseria-PilC (superfamily) domain of the tip-associated adhesin, while PilW of the superfamily of putative TfP assembly proteins and PilV belongs to the superfamily of TfP assembly protein. Also, the analyses suggested the presence of specific functional domains involved in adhesion, energy transduction and signaling functions. The phylogenetic analysis indicated that the PilY1 of Acidithiobacillus genus forms a cohesive group linked with iron- and/or sulfur-oxidizing microorganisms from acid mine drainage or mine tailings. This work enriches knowledge regarding colonization, adhesion and biooxidation of inorganic sulfurs by A. thiooxidans.

A bioelectrochemical study of charge transfer in the biofilm/chalcopyrite interface was performed to investigate the effect of surficial sulfur reduced species (SRS), as non-stochiometric compounds or polysulfides (Sn2-), and elemental sulfur (S0) on a biofilm structure during the earliest stages (1, 12 and 24 h) of chalcopyrite biooxidation by A. thiooxidans alone and adding Leptospirillum sp. The surface of massive chalcopyrite electrodes was exposed to the bacteria, which were analyzed electrochemically, spectroscopically, and microscopically. At the studied earlier times, charge transfer and significant differences in the biofilm structure were detected, depending on the presence of Leptospirillum sp. acting on A. thiooxidans biofilms. Such differences were a consequence of a continuous chalcopyrite pitting and promoting changes in biofilm hydropathy. A. thiooxidans modifies the reactive properties of SRS and favors an acidic dissolution, which shifts into ferric when Leptospirillum sp. is present. A. thiooxidans allows H+ and Fe3+ diffusion, and Leptospirillum sp. allows surpassing the charge transfer (reactivity) barrier between the mineral interface and the ions. The observed changes of hydropathy on the interface are associated to ions and electrons activity and transfer. Finally, a model of S0 biooxidation by A. thiooxidans alone or with Leptospirillum sp., is proposed.

Total and bioaccessible concentrations of arsenic (As) and lead (Pb), as well as their bearing phases in the adjacent soil area (residential area) of the historic and active Fe-oxide-rich mining district of Cerro de Mercado, Durango (Mexico), were evaluated. Results indicated the presence of arsenopyrite, galena, and As-bearing phases in ultrafine (

The diatom silicified cell wall (frustule) contains pore arrays at the micro- to nanometer scale that display efficient luminescence within the visible spectrum. Morphometric analysis of the size and arrangement of pores was conducted to observe whether any correlation exists with the photoluminescence (PL) of two diatom species of different ages. UV-excited PL displays four clearly defined peaks within the blue-region spectrum, on top of the broad PL characteristic of synthetic porous silicon dioxide, recorded for reference and where discrete lines are absent. A set of shifted emission lines was observed when diatom cultures reached adulthood. These discrete line shifts correlate with structural changes observed in adult frustules: reduction in pore diameter; appearance of pores within pores, 10 nm in size; an increase in the gap distance between stria; and the deposition of several girdle bands with a concomitant increase in the diatom waist length, as well as the appearance of pores on such bands. Destruction of the pores results in the disappearance of all discrete emission lines. The PL shifts are correlated with a substantial increment of Si–OH groups adsorbed on the frustule surface, as revealed by Fourier transform infrared spectroscopy. Copyright © 2014 John Wiley & Sons, Ltd.

Massive pyrite (FeS2) electrodes were potentiostatically modified by means of variable oxidation pulse to induce formation of diverse surface sulfur species (S n 2−, S0). The evolution of reactivity of the resulting surfaces considers transition from passive (e.g., Fe1−x S2) to active sulfur species (e.g., Fe1−x S2−y , S0). Selected modified pyrite surfaces were incubated with cells of sulfur-oxidizing Acidithiobacillus thiooxidans for 24 h in a specific culture medium (pH 2). Abiotic control experiments were also performed to compare chemical and biological oxidation. After incubation, the attached cells density and their exopolysaccharides were analyzed by confocal laser scanning microscopy (CLMS) and atomic force microscopy (AFM) on bio-oxidized surfaces; additionally, S n 2−/S0 speciation was carried out on bio-oxidized and abiotic pyrite surfaces using Raman spectroscopy. Our results indicate an important correlation between the evolution of S n 2−/S0 surface species ratio and biofilm formation. Hence, pyrite surfaces with mainly passive-sulfur species were less colonized by A. thiooxidans as compared to surfaces with active sulfur species. These results provide knowledge that may contribute to establishing interfacial conditions that enhance or delay metal sulfide (MS) dissolution, as a function of the biofilm formed by sulfur-oxidizing bacteria.

The diatom silicified cell wall (frustule) contains pore arrays at the micro- to nanometer scale that display efficient luminescence within the visible spectrum. Morphometric analysis of the size and arrangement of pores was conducted to observe whether any correlation exists with the photoluminescence (PL) of two diatom species of different ages. UV-excited PL displays four clearly defined peaks within the blue-region spectrum, on top of the broad PL characteristic of synthetic porous silicon dioxide, recorded for reference and where discrete lines are absent. A set of shifted emission lines was observed when diatom cultures reached adulthood. These discrete line shifts correlate with structural changes observed in adult frustules: reduction in pore diameter; appearance of pores within pores, 10 nm in size; an increase in the gap distance between stria; and the deposition of several girdle bands with a concomitant increase in the diatom waist length, as well as the appearance of pores on such bands. Destruction of the pores results in the disappearance of all discrete emission lines. The PL shifts are correlated with a substantial increment of Si-OH groups adsorbed on the frustule surface, as revealed by Fourier transform infrared spectroscopy.

Surfaces of massive chalcopyrite (CuFeS2) electrodes were modified by applying variable oxidation potential pulses under growth media in order to induce the formation of different secondary phases (e.g., copper-rich polysulfides, S n 2−; elemental sulfur, S0; and covellite, CuS). The evolution of reactivity (oxidation capacity) of the resulting chalcopyrite surfaces considers a transition from passive or inactive (containing CuS and S n 2−) to active (containing increasing amounts of S0) phases. Modified surfaces were incubated with cells of sulfur-oxidizing bacteria (Acidithiobacillus thiooxidans) for 24 h in a specific culture medium (pH 2). Abiotic control experiments were also performed to compare chemical and biological oxidation. After incubation, the density of cells attached to chalcopyrite surfaces, the structure of the formed biofilm, and their exopolysaccharides and nucleic acids were analyzed by confocal laser scanning microscopy (CLSM) and scanning electron microscopy coupled to dispersive X-ray analysis (SEM-EDS). Additionally, CuS and S n 2−/S0 speciation, as well as secondary phase evolution, was carried out on biooxidized and abiotic chalcopyrite surfaces using Raman spectroscopy and SEM-EDS. Our results indicate that oxidized chalcopyrite surfaces initially containing inactive S n 2− and S n 2−/CuS phases were less colonized by A. thiooxidans as compared with surfaces containing active phases (mainly S0). Furthermore, it was observed that cells were partially covered by CuS and S0 phases during biooxidation, especially at highly oxidized chalcopyrite surfaces, suggesting the innocuous effect of CuS phases during A. thiooxidans performance. These results may contribute to understanding the effect of the concomitant formation of refractory secondary phases (as CuS and inactive S n 2−) during the biooxidation of chalcopyrite by sulfur-oxidizing microorganisms in bioleaching systems.

Photosynthetic biofilms successfully colonize the sediments of a mine tailings reservoir (Guanajuato, Mexico) despite the high metal concentrations that are present. To elucidate the mechanisms of biofilm survival despite metal ores, experiments were performed to evaluate the response of seminatural biofilms to Cu, Zn, and a combination of both metals at concentrations observed in the field. The biofilms were composed mostly of the chlorophyte Chlorococcum sp. and the cyanobacterium Phormidium sp., and their response to the two added metals was described by measurements of extracellular polymeric substances (EPS) and in vivo fluorescence. The photosynthetic efficiency and the minimal chlorophyll fluorescence of dark-adapted cells were measured by multiwavelength pulse amplitude-modulated fluorometry. The photosynthetic efficiency of light-adapted cells (phi(PSII)) also was measured. Metal exposure increased the EPS production of biofilms, as visualized with confocal laser-scanning microscopy. Extracellular polymeric substances enhanced the extracellular metal accumulation from the first day of metal exposure. Metals provoked changes in the relative abundance of the dominant taxa because of a species-specific response to the metals when added individually. Metals affected the phi(PSII) less than the total biomass, suggesting ongoing activity of the surviving biofilms. Survival of individual biofilm photosynthetic cells was found to resume from the embedding in the mucilaginous structure, which immobilizes the metals extracellularly. The survival of biofilms under mixed-metal exposure has practical applications in the remediation of mine tailings.

"The aims of this research are to identify and describe a periphyton community of thermophilic microalgae in order to expand our knowledge on biodiversity of a particular environment. Conspicuous biomass of thermophilic microalgae (48 ◦ C) inhabits the cooling towers of the thermoelectric power plant of Villa de Reyes (Central Mexico). Aggregate samples or microalgal mats were taken in three different areas of the top of a cooling tower, for identification. According to the sequencing analysis of 16S and 18S rDNA genes, the community is dominated by 3 species of Cyanoprokaryota: Chlorogloeopsis fritschii , Arthronema africanum and Chroococcidiopsis sp., previously reported as thermophiles. Also, 2 species of the Chlorophyte or green algae Scenedesmus . Finally, 12 species of diatoms comprise the microalgal community; diatoms were only microscopically identified within the mats, suggesting that the mats constitute a suitable microenvironment in thermal ambiences. The identified species are of particular interest because their habitat represents an extreme and an artificial biotope. To the best of our knowledge, this is the first report of thermophilic communities of microalgae in Mexico from a power plant; also, this is the first report of A. africanum for the country. All Rights Reserved © 2016 Universidad Nacional Autónoma de México, Instituto de Biología. This is an open access item distributed under the Creative Commons CC License BY-NC-ND 4.0."